HOLLYWOOD – Screenwriter Kayla Alpert (“Confessions of a Shopaholic”) was handed a choice assignment in adapting “Flowers in the Attic,” V.C. Andrews’ 1979 novel about the darkest possible family stuff, into a Lifetime movie.

Also some pressure. The book has sold more than 40 million copies and is a semi-secret touchstone for a generation of women who made it the tween “50 Shades of Grey” of its day. The Lifetime movie, which stars Heather Graham (“Scrubs”), Kiernan Shipka (“Mad Men”) and Ellen Burstyn (“Big Love”), airs at 7 p.m. Saturday (Jan. 18).

“I did feel a lot of pressure,” Alpert said at the Winter TV Tour. “Luckily, the process of writing is you sitting alone in a room. So the pressure is not from the outside but from the inside. Lifetime was really great about just leaving me alone and calling me every few weeks and saying, ‘When are we getting the script? When are we getting the script?’”

And, of course, she had the book as a map. A 1980s movie adaptation strayed too far from Andrews’ story for many fans of the book. Alpert’s script is an attempt at a more faithful pass at source material that deals in a lot of forbidden themes and dreams.

Alpert was faithful to a point. It is a basic-cable-TV movie, after all, aimed at Lifetime’s female core viewership. Though many in that core are presumably familiar with the book, some of its details don’t make the journey to explicit pictures.

“Lifetime was really supportive of just staying true to the material,” Alpert said. “There was a lot of condensing that we had to do. It’s a really kind of long, epic book even though it only takes place over the course of three years. So we had to pick and choose our moments. It’s actually more fun being less explicit. We had to get a little creative.

“It’s really juicy, and it’s really compelling. It’s kind of a writer’s dream, and especially because I was such a fan of the book. And it was fun going back and remembering some of those crazy scenes that I had sort of repressed. It was a blast. I feel like we really went for it. We really did not pull any punches.”

The network’s new adaptation of “Flowers in the Attic,” V. C. Andrews’s best-selling 1979 novel about bad parenting, whips and the love that dare not take a DNA test, is what it is — a movie of the week, plopping off the assembly line with a little more gothic atmosphere than usual and some expensive accessories. These consist of Heather Graham, Ellen Burstyn and the up-and-coming Kiernan Shipka, who goes from playing an unhappy daughter in “Mad Men” to playing a really unhappy daughter here.

The bookish girls I knew in seventh grade, circa 1980, dropped Laura Ingalls Wilder like a rock in Plum Creek for “Flowers in the Attic,” a creepy novel by V.C. Andrews that has sold some 40 million copies worldwide, spawning a 1987 movie version that met with disapproval from fans. Among other letdowns, I reckon, the movie left out the book’s scenes of brother-sister incest.

So Lifetime is taking another, long-overdue stab at a “Flowers in the Attic” movie Saturday night — and this time the incest has been included, so, uh, hooray?

Fans of V.C. Andrews’ best-selling potboiler “Flowers in the Attic” have been waiting more than 30 years for a faithful screen adaptation. They’ll get that, but not much more from this lackluster Lifetime production toplining precocious “Mad Men” scene-stealer Kiernan Shipka in her first leading role. Lacking either the Gothic atmosphere that could have transformed trashy material into something truly chilling or an over-the-top camp factor that would’ve ensured a lowbrow guilty pleasure, “Flowers” has to rely on a mix of nostalgia and curiosity to draw in viewers, or risk seeing plans for an already-in-development sequel wither on the vine.